The objective of these studies is to determine the molecular and cellular interactions that lead to the selective expression of IgA in secretory glands and to the selective transport of IgA into external secretions. The structural basis of the binding of immunoglobulins to specific receptors on epithelial cells will be investigated and we shall attempt to identify and characterize the immun globulin binding receptor. Properties of unstimulated and mitogen-stimulated colostral lymphocytes will be determined. With the use of immunofluorescence techniques, we shall determine the intracellular and membrane-associated immunogl bulin class. The presence of receptors for secretory component will be determined by immunofluorescence on the membrane and in cytoplasm of stimulated and unstimulated lymphocytes. The effect of co-cultivation of peripheral bl od or col stral lymphocytes and normal or tum r epithelial cells on the expression of the immunoglobulin isotype will be studied. With the use of physicochemical techniques, conformational studies will be made of constituent components of secretory IgA molecules.